Back to EveryPatent.com
United States Patent |
6,256,954
|
Thooft
|
July 10, 2001
|
Combination reinforcement for floor on piles
Abstract
A fixed construction (10) comprises rigid piles (12) and a monolithic
concrete floor slab resting (14) on the piles. The floor slab comprises
straight zones connecting in the two directions, i.e. lengthwise and
broadwise, the shortest distance between the areas of the floor slab above
the piles. The floor slab (14) is reinforced by a combination of: (a)
fibers (22) distributed over the volume of the floor slab (14); (b) and
steel rods (16, 16') with a yield strength of at least 690 MPa and being
located in those straight zones.
This construction reduces considerably the amount of reinforcement steel,
increases the bearing capacity and enables to reduce the time for making
such a construction.
Inventors:
|
Thooft; Hendrik (Zingem, BE)
|
Assignee:
|
N.V. Bekaert S.A. (Zwevegem, BE)
|
Appl. No.:
|
290244 |
Filed:
|
April 13, 1999 |
Foreign Application Priority Data
Current U.S. Class: |
52/299; 52/294; 52/296; 52/649.1; 52/649.2; 405/229 |
Intern'l Class: |
E02D 005/34 |
Field of Search: |
52/299,294,296,649.1,649.2
405/229,230,231,256
|
References Cited
U.S. Patent Documents
776419 | Nov., 1904 | Platt.
| |
1363273 | Dec., 1920 | Ruff | 52/299.
|
2413562 | Dec., 1946 | Henderson | 52/296.
|
2998216 | Aug., 1961 | Hurd | 52/294.
|
3087308 | Apr., 1963 | Hart et al.
| |
3184893 | May., 1965 | Booth.
| |
3706168 | Dec., 1972 | Pillish | 52/294.
|
3918229 | Nov., 1975 | Schweinberger | 52/296.
|
4007568 | Feb., 1977 | Soble | 52/294.
|
4031687 | Jun., 1977 | Kuntz.
| |
4275538 | Jun., 1981 | Bounds | 52/299.
|
4594825 | Jun., 1986 | Lamarca | 52/294.
|
4799348 | Jan., 1989 | Brami et al.
| |
4886399 | Dec., 1989 | Pidgeon.
| |
4899497 | Feb., 1990 | Madl, Jr.
| |
5337533 | Aug., 1994 | Kajita | 52/294.
|
5367845 | Nov., 1994 | Hartling | 52/294.
|
5699643 | Dec., 1997 | Kinard | 52/742.
|
Foreign Patent Documents |
29 52 783 | Jul., 1981 | DE.
| |
0 121 003 | Oct., 1984 | EP.
| |
1105259 | Nov., 1955 | FR.
| |
2112508 | Jun., 1972 | FR.
| |
2160180 | Jun., 1973 | FR.
| |
2220643 | Oct., 1974 | FR.
| |
252975 | Jun., 1926 | GB.
| |
WO 95/35415 | Dec., 1995 | WO.
| |
WO 98/36138 | Aug., 1998 | WO.
| |
Other References
European Search Report (Application No. EP 98 20 1955).
|
Primary Examiner: Friedman; Carl D.
Assistant Examiner: A; Phi Dieu Tran
Attorney, Agent or Firm: Shlesinger, Arkwright & Garvey LLP
Claims
What is claimed is:
1. A fixed constructions, comprising:
a) rigid piles and a monolithic concrete floor slab resting on said piles,
said rigid piles being arranged in a regular rectangular pattern where
each set of four piles forms a rectangles;
b) said floor slab comprising straight zones connecting in both the
lengthwise and broadwise directions, the shortest distance between those
areas of the floor slab above the piles;
c) said floor slab being reinforced by a combination of:
i) fibres being distributed over the volume of said floor slab; and
ii) steel rods having a yield strength of at least 690 MPa and being
located only in said straight zones.
2. A fixed construction according to claim 1 wherein said steel rods are
arranged in pairs.
3. A fixed construction according to claim 2 wherein one of said pairs is
located in each of said straight zones.
4. A fixed construction according to claim 2 wherein the rods of each pair
are transversely connected with each other by means of a transverse steel
element.
5. A fixed construction according to claim 1 wherein said rods are
supported by means of a spacer.
6. A fixed construction according to claim 1 wherein said floor slab is a
jointless floor slab.
7. A fixed construction according to claim 1 wherein said floor slab
directly rests on said piles.
8. A fixed construction according to claim 1 wherein said fibres are steel
fibres.
9. A fixed construction according to claim 1 wherein said steel rods occupy
up to 0.4% of the total volume of said floor slab.
10. A fixed construction according to claim 8 wherein said steel fibres
occupy at most 60 kg/m.sup.3 (=0.75 volume %) of the floor slab.
11. A fixed construction according to claim 8 wherein said steel fibres and
said steel rods together occupy at most 1.5 volume % of the floor slab.
12. A fixed construction according to claim 3, wherein the rods of each
pair are transversely connected with each other by means of a transverse
steel element.
13. A fixed construction according to claim 2 wherein said rods are
supported by means of a spacer.
14. A fixed construction according to claim 2 wherein said floor slab is a
jointless floor slab.
15. A fixed construction according to claim 2 wherein said floor slab
directly rests on said piles.
16. A fixed construction according to claim 2 wherein said fibres are steel
fibres.
17. A fixed construction according to claim 2 wherein said steel rods
occupy up to 0.4% of the total volume of said floor slab.
18. A fixed construction according to claim 9 wherein said steel fibres
occupy at most 60 kg/m.sup.3 (=0.75 volume %) of the floor slab.
19. A fixed construction, comprising:
a) rigid piles;
b) a concrete floor slab resting on the rigid piles;
c) four of the rigid piles being arranged in a rectangular pattern;
d) straight zones extending between adjacent ones of the four piles, the
straight zones extending in lengthwise and broadwise directions;
e) fibers being distributed throughout the volume of the concrete floor
slab; and
f) steel rods having a yield strength of at least about 690 MPa being
provided in the floor slab, the steel rods being located only in the
straight zones.
20. A fixed construction according to claim 19, wherein:
a) said steel rods include pairs of steel rods.
21. A fixed construction according to claim 19, wherein:
a) the concrete floor slab rests directly on the piles.
22. A fixed construction according to claim 19, wherein:
a) the fibers are steel fibers.
Description
FIELD OF THE INVENTION
The present invention relates to a fixed construction which comprises rigid
piles and a monolithic concrete floor slab.
BACKGROUND OF THE INVENTION
Concrete industrial floor slabs usually rest via a foundation layer on a
natural ground. Unevenly distributed loads on top of the floor slab are
transmitted via the floor slab and the foundation layer in a more evenly
distributed form through to the natural ground, which eventually bears the
load.
Natural grounds of an inferior quality, e.g. characterized by a Westergaard
K-value of less than 10 MPa/m, are first dug up and/or tamped down and
leveled before the foundation is laid over it.
Due to the fact that a lot of natural grounds of good quality
(characterized by a high Westergaard K-value) have already been taken for
existing constructions, the number of natural grounds with inferior or
even unacceptable quality (i.e. with a low Westergaard K-value) which are
being considered for constructions is increasing. The bearing capacity of
some grounds is so bad that digging up and/or excavating and/or tamping
down would constitute an enormous amount of work and cost.
In such a case it is known to rest the floor slab on driven or bored piles.
Placing a floor slab on driven or bored piles under load, however, creates
very high negative peak moments in the areas above these piles and
relatively much lower (about one fifth of the height of the peak moments)
positive moments in the zones between the piles. Reinforcing floor slabs
on driven or bored piles with uniformly distributed steel fibres would not
be economical since the zones between the piles would have a quantity of
steel fibres which is unnecessarily too high and which would cause trouble
during the pumping and pouring of the concrete and would render the
solution not economical.
This problem has been solved in FR 2 718 765 of applicant, by having the
floor slab rest on a number of gravel columns. As has been explained
therein, these gravel columns are not as rigid as common piles and
compress relatively easily under a downward load (the compression modulus
of gravel columns e.g. ranges from 0.2 to 0.4 MN/cm) so that the gravel
columns function like a spring in a mathematical model, which means that
the floor slab is no longer subjected to high bending deformations in the
zones above the columns.
In the international application PCT/EP98/00719 of applicant a solution has
been disclosed to the above-mentioned problem. The present invention
involves an improvement of the invention disclosed in this international
application.
SUMMARY OF THE INVENTION
The present invention provides an alternative reinforcement for concrete
floor slabs resting on piles which saves weight of steel and which
prevents introduction of high amounts of steel fibres into the floor slab.
Another object of the present invention is to provide a reinforcement for
concrete floor slabs resting on piles where the reinforcement functions as
a tensile anchor for taking up shrinkage cracks.
Still another object of the present invention is to save time in
constructing a concrete floor slab resting on piles.
In comparison with the invention disclosed in PCT/EP98/00719, the present
invention provides a greater weight savings in steel and a greater and
more reduction in time required to construct the concrete floor.
According to the present invention there is provided a fixed construction
which comprises rigid piles and a monolithic concrete floor slab which
rests on the piles. The rigid piles are arranged in a regular rectangular
pattern, i.e. each set of four piles forms a rectangle. The floor slab
comprises straight zones which connect the shortest distance between the
areas of the floor slab above the piles. The width of such zones ranges
from 50% to 500% the largest dimension of the piles. These straight zones
run both lengthwise and broadwise. The term "lengthwise" refers to the
direction of the longest side and the term "broadwise" refers to the
direction of the smallest side. If, such as is often the case, the longest
side is about equal to the shortest side, the terms broadwise and
lengthwise are arbitrarily designated to the two directions.
The floor slab is reinforced by a combination of:
(a) fibres which are distributed over the volume of the floor slab;
(b) steel bars with a yield strength above 690 MPa and which are located in
those straight zones, and preferably only in those straight zones, which
means that outside these zones there is no substantial reinforcement
except for the fibres under (a).
The term "rigid piles" refers to piles the compression modulus of which is
much greater than the compression modulus of gravel columns and is much
greater than 10 MN/cm. These rigid piles are driven or bored piles and may
be made of steel, concrete or wood. They may have a square cross-section
with a side of 20 cm or more, or they may have a circular cross-section
with a diameter ranging between 25 cm and 50 cm. The distance between two
adjacent piles may vary from 2.5 m to 6 m.
The term "yield strength" is herein defined as the strength at a permanent
elongation of 0.2%.
By using this combination reinforcement constituted by fibres and a
classical steel rod reinforcement which is only located in the critical
points of the floor slab, it has proved to be possible to limit the total
amounts of steel fibres in the concrete slab from about 120 kg/m.sup.3
(=1.53 vol. %) until a concentration ranging from about 30 kg/m.sup.3
(=0.38 vol. %) to about 80 kg/m.sup.3 (=1.02 vol. %), or even lower.
A floor slab is an industrial floor with dimensions up to 60 m.times.60 m
and more, and--due to the continuous rod reinforcement--carried out
without joints, i.e. without control joints, isolation joints,
construction joints or shrinkage joints.
The thickness of the floor slab may range from about 14 cm to 35 cm and
more.
Of course, in order to cover large surfaces more than one such a jointless
floor slab may be put adjacent to each other. With the present invention,
i.e. with the combination of both fibres and continuous rods it has proved
possible to eliminate expansion joints when constructing such a second
(and a third . . .) jointless floor slab adjacent to the first one. This
is done by reinforcing the transition zone from one floor slab to the
other by means of a metal netting.
Preferably the floor slab "directly" rests on the piles. This refers to a
floor slab which rests on the piles without any intermediate beams or
plates. All reinforcement is embedded in the floor slab itself.
The fibres in the floor slab are preferably uniformly distributed in the
concrete of the floor slab. The fibres may be synthetic fibres but are
preferably steel fibres, e.g. steel fibres cut from steel plates or, in a
preferable embodiment, hard drawn steel fibres. These fibres have a
thickness or a diameter varying between 0.5 and 1.2 mm, and a
length-to-thickness ratio ranging from 40 to 130, preferably from 60 to
100. The fibres have mechanical deformations such as ends as hook shapes,
thickenings or undulations in order to improve the anchorage to the
concrete. The tensile strength of the steel fibres ranges from 800 to 3000
MPa, e.g. from 900 to 1400 MPa. The amount of steel fibres in the floor
slab of the invention preferably ranges from 30 kg/m.sup.3 (0.38 vol. %)
to 80 kg/m.sup.3 (1.02 vol. %), e.g. from 40 kg/m.sup.3 (0.51 vol. %) to
65 kg/M.sup.3 (0.83 vol. %). So the amount of steel fibres in a concrete
floor slab according to the invention is preferably somewhat higher than
steel fibre reinforced floors on natural ground of good quality (normal
amounts up to 35 kg/m.sup.3), but can be kept within economical limits due
to the combination with the higher tensile steel rod reinforcement.
The other steel reinforcement in addition to the steel fibres, the steel
rods'are preferably hard drawn and occupy maximum 0.4% of the total volume
of the floor slab, e.g. maximum 0.3%, e.g. only 0.2% or 0.3%. The diameter
of the steel rods ranges from about 3.5 mm to about 12.0 mm.
The minimum yield strength of the steel rods is 690 MPa, but higher values
of this yield strength are obtainable, particularly for rods with smaller
diameters. Yield strengths of 800 MPa, 1000 MPa and 1200 MPa are
obtainable.
Both steel reinforcements, the steel fibres and the steel rods, preferably
occupy maximum 1.5% of the total volume of the floor slab, e.g. maximum
1.2%.
In a preferable embodiment of the present invention, the steel rods are
arranged in pairs. For example, in each of the straight zones one pair of
rods is located.
The rods of each pair are parallel and may be connected by means of
transverse steel elements. These transverse steel element are conveniently
made of a softer steel, i.e. a steel with a carbon content which is lower
than the carbon content of the steel rods. This allows one to make perfect
welded joints between the transverse steel elements and the steel rods. In
this way the combination longitudinal rod--transverse steel element forms
a "bi-steel strip".
The transverse steel elements may be round in cross-section or flat. In the
latter case, the flat face forms a right angle with the longitudinal axis
of the rods. The flat face prevents a transmission of oblique forces to
the concrete.
The presence of the transverse steel elements helps to improve the
anchorage in the concrete.
The distance between two parallel rods in each pair is about the same order
of magnitude as their diameter, about equal for rods with a diameter of
more than 20 mm, but not less than 20 mm for rods with a diameter less
than 20 mm. A spacing ranging between 20 mm and 30 mm is suitable in most
circumstances. Typical values are 20 mm and 23 mm.
The interval between the transverse steel elements is usually higher than
the distance between the longitudinal rods but does not exceed 200 mm. A
typical value is 95 mm.
Preferably the pair of rods are placed and supported by means of spacers
which can be made of a synthetic material.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described into more detail with reference to the
accompanying drawings wherein
FIG. 1 is a transverse cross-sectional view of a fixed construction
according to the invention according to line 1--1 of FIG. 2;
FIG. 2 is a cross-sectional view of the fixed construction according to
line II--II of FIG. 1
FIG. 3 is a perspective view of a bi-steel strip;
FIG. 4 shows how bi-steel strips can be supported by means of a spacer.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION.
Referring to FIG. 1, a fixed construction according to the invention
comprises rigid piles 12 which are driven or bored into the natural ground
13. A concrete floor slab 14 directly rests on the piles 12, i.e. without
any intermediate plate or beam. The invention is particularly interesting
for use on natural grounds of an inferior quality, i.e. with a Westergaard
K-value of less than 10 MPa/m. In course of time, such natural grounds
settle to a relatively high degree and no longer provide an adequate
support for the floor slab 14. This is outlined by a distance 15 in FIG.
1. So the piles 12 remain the only reliable support for the floor slab 14.
FIG. 2 illustrates where the rod reinforcement is located in the floor slab
14. Steel rods 16, running lengthwise, and steel rods 16', running
broadwise, connect the shortest distance above those areas 18 of the floor
slab which are situated above the piles 12. So the steel rods not only
reinforce the limited areas 18 above the piles 12 but also the straight
zones 19 between the piles 12. As has been explained hereabove, the
moments occurring between the piles are not as high as those occuring in
the zones above the piles (only 35% of the peak moments above the piles).
Experiments have proved that reinforcing the straight zones 19 between the
piles by means of the steel rods, as in the present invention, helps to
stop and limit cracks which are a consequence of shrinkage of the concrete
of the floor slab or which are a consequence of loads on the floor slab.
More particularly, reinforcing the straight zones 19 between the piles and
placing the floor slab under increasing loads, leads to a pattern where
the cracks are more spread and multiplied in comparison with a floor slab
where only steel fibres are present as reinforcement. Due to this
spreading and multiplication, the cracks are limited and are less harmful.
According to FIG. 2, steel fibres or fibers 22 are distributed, preferably
as uniformly as possible in the two horizontal directions over the whole
volume of the floor slab 14.
As may be derived from FIG. 2, the present invention makes efficient use of
both reinforcement means: the steel rods 16 and the steel fibres 22. In
the most critical zone (peak moments=100%), namely area 18 above the
piles, the steel rods 16 are present in a double way since they cross each
other and steel fibres 22 are present. In the second most critical zone
(moments=35% of the peak moments above the piles), namely the straight
zones 19 between the piles, steel rods 16 (in a single way) and steel
fibres 22 are present. Outside the area 18 and outside the straight zones
19 (moments=only 20% of the peak moments above the piles) only steel
fibres 22 are present.
FIG. 3 gives a perspective view of a bi-steel strip 23 made from two
parallel wire rods 16. The parallel wire rods 16 are connected by means of
transverse flat steel elements 24 which are welded to the wire rods 16.
FIG. 4 illustrates how steel rods 16 and 16' are placed and supported by
means of a spacer 26 which can be made of a synthetic material.
Coming back to FIG. 2, a fixed construction 10 according to the invention
can be made as follows. Rigid piles 12 are driven or bored into the
natural ground 13. The natural ground 13 is leveled and plastic spacers 26
are placed in the areas 18 above the piles 12. Normally, two to three
spacers 26 are used every meter or four to five spacers 26 are used every
square meter. The bi-steel strips 23 are placed above the spacers 26 as
illustrated in FIG. 4. Finally, concrete with steel fibres 22 is pumped
and poured over the designed area.
The concrete used may be conventional concrete varying from C20/25 to
C40/50 according to the European norms (EN 206). The characteristic
compressive strength after 28 days of such a concrete varies between 20
MPa and 40 MPa if measured on cylinders (300.times..O slashed.150 mm ) and
between 25 and 50 MPa if measured on cubes (150.times.150.times.150 mm).
After being poured the concrete is first leveled and then left to harden.
The finishing operation may comprise the power floating of the surface in
order to obtain a flat floor with a smooth surface and may also comprise
applying a topping (e.g. dry shake material) over the hardening floor slab
and curing the surface by means of waxes (curing compounds) . The
hardening may take fourteen days or more during which no substantial loads
should be put on the floor slab.
In comparison with a concrete floor slab where only steel fibres have been
used as a reinforcement, a fixed construction according to the invention
has led to a construction with an increased bearing capacity and/or to a
construction where the distance between the supporting piles may be
increased.
The inventors have discovered that with the combination reinforcement
according to the invention, there is no need to place additional
reinforcements such as still some more steel rods or steel meshes in the
areas of the floor slab above the piles.
The inventors have also discovered that with the combination reinforcement
according to the invention there is no need to construct the piles with an
increased cross-section at their top and that there is neither a need to
construct separate pile heads with an increased cross-section.
Such increased cross-sections just under the floor slab are used in
existing constructions to diminish the transversal forces of loads on the
slab. The present invention decreases this necessity.
In comparison with a combination reinforcement of steel rebars of
conventional yield strength and steel fibres, the present invention allows
to decrease the volume of steel rods required by an amount ranging from 2%
to 15% and more, depending upon the particular floor to be reinforced.
Top